U.S. Pat. No. 5,707,331 (Wells) discloses a decanting centrifuge for separating through centrifugation two or more components of blood. The Wells patent teaches the use of a removable, disposable processing unit that has two fluid chambers. The processing unit is received in a centrifuge apparatus that can hold the processing unit selectively in particular orientations whereby supernatant fluids can be transferred from one chamber to another by way of gravity draining or centrifugal transfer.
The Wells patent does not describe structure for limiting vibrations of the centrifuge arising from imbalances in the rotor, and the Wells centrifuge is, accordingly susceptible to such vibrations. Imbalance in the Wells system typically occurs when the volume of blood placed in the processing unit is greater or less than the design volume. For example, a typical centrifuge according to the Wells system may be designed to process 50 ml of blood, whereas the user may actually place 20 ml to 60 ml in the processing unit. Such a differential in the amount of blood is significant, and forces caused by this imbalance arise during centrifugation.
While vibration-isolating structures are known, they are placed in the centrifuge such that absorption of the imbalance forces creates torque on the rotor shaft, which must then be absorbed also. Thus, an inexpensive and efficient structure for absorbing imbalance forces is desirable.
The Wells patent also describes structure for holding the processing unit in a desired orientation. In the disclosed embodiment, a movable plate is designed to engage a part of a support frame that supports the processing disposable. That plate is electrically or magnetically driven between two vertical positions. In the lowered position, the plate does not contact the support frame, and the processing disposable swings freely during centrifugation. In a second position, the plate engage the frame to hold the processing disposable in a tilted orientation whereby supernatant in one of the chambers drains into a second of the chambers. In yet another position, the plate engages the frame to hold the processing disposable in an orientation whereby supernatant is centrifugally transferred from one chamber to another.
The movable plate in the Wells patent rotates with the rotor, and there is no relative movement in the circumferential direction between the plate and the support frame. This prevents wear of the support frame or the plate that would result from such relative motions but, at the same time, requires more complex structure to control the vertical positions of the rotating plate. Reducing the complexity of this structure is desirable.
Accordingly, there is a need for a centrifuge that relies upon less expensive structures and reduces vibrations.